Leads on Stancor A-3801

[BasementJames]

Hi,

A friend of mine came into a Stancor A-3801. I offered to install it in a TW clone, but upon receiving it, I'm a bit confused.

The examples of the A-3801 I have generally seen have a grey bell, PVC wires and a convenient diagram showing the color codes on the bell.

This has none of that.

First off, can anyone share any information about this particular model? I understand there were different runs and even versions of the A-3801.
This appears to be a very early one given the cloth wire.

Second, does anyone know how I would go about determining which lead is which?
On the primary, I need to find the center tap and on the secondary, I need to figure out respective impedances.
I lack the education.


Thanks in advance.

[didit]

Hello --

This label was doubtless on your transformer when it left the factory.

Stancor A-3801 wiring label.jpg

The trio of wires on one side are the primary. Red is the centre tap. You'll need to sort the other two by carefully poking at the colours or simply wire it up and solve the NF issues once it's running. The other side has all the secondaries and you'll need to poke carefully and hopefully for the faded and stained colours. Or perhaps seek out guidance on reading those with a multimeter.

Best ..

[BasementJames]

Thanks for the tip.

The one I'm holding has five wires on the secondary vs the six on the drawing.
Although both are a model A-3801, I'm not sure we are looking at the same transformers.

On the primary side of the one I am holding, I would guess the colors to be green, red, yellow.

I have done some research on how to figure this out with a multimeter and poked around a bit looking at resistance.
On the primary
Green to Red = 64.7 ohms
Red to Yellow = 57.8 ohms
Green to Yellow = 122.1 ohms

I would guess red is the common?

Then on the secondary it seems like some voltage needs to be applied and then measured.
I need to look into that.

This would be replacing a perfectly working Ceriatone transformer and I want to be sure it is actually worth it.

[didit]

You've mapped the primary correctly. Suggest what appears today as green began 60+ years ago as blue. Uncertain about the secondary lead count. There are Stancor catalogues floating around and perhaps an even older build had one fewer tap or perhaps that transformer was slightly damaged sometime in the past 60+ years. If you can determine which is one is the brown "common" and have a good quality multimeter it's possible to determine the line up of the secondary taps via resistance. Alternatively it's also practical to energize the the primary (filament AC voltage is common advice) then you should be able to map the taps with AC voltage measurements.

..